The invention discloses a preparation method of S-carboxymethyl-L-
cysteine, which relates to the field of
amino acid production, and mainly comprises the following steps: 1, dissolving L-
cysteine hydrochloride monohydrate, cooling the solution to 0-5 DEG C, and regulating the pH value to 9-10 to obtain a solution (a); 2, dissolving
chloroacetic acid, and adjusting the pH value to 6-7 to obtain a solution (b); 3, dropwise adding the solution (b) into the solution (a), and carrying out heat preservation to obtain a solution (c); 4, adjusting the pH value of the solution (c) to 8, and heating thesolution to react for 1 hour; 5, cooling the solution (c) to
room temperature, adjusting the pH value to 5.5, and filtering the solution; 6, adjusting the pH value of the filtrate to 2.5-3.0, refrigerating the filtrate overnight, carrying out suction
filtration, and
drying the filtrate to obtain a crude product; 7, dissolving the crude product to obtain a solution (d), and acidifying the solution(d) to an
isoelectric point; 8, adding a
seed crystal into the solution (d), and adjusting the solution (d) to an
isoelectric point; 9, purifying a finish product. By means of the preparation method,S-carboxymethyl-L-
cysteine with
large particle size,
high density and high purity can be obtained, and the preparation method is suitable for being used in multiple fields.